Etudes géochimiques et geomorphologie lacustre du bassin du lac Yakhi en Mongolie orientale

Abstract

This study presents the landscape evolution of Lake Yakhi basin in eastern Mongolia where the lake plays an important role in the surface water resources. The multiple paleoshoreline features indicate wave-cut terraces, whereas the modern-day shorelines show that Lake Yakhi is at rapid northward regression. The paleo- and modern-day shorelines imply that the paleo-Lake Yakhi may have covered an extensive area with different hydrological conditions in the past. Lake Yakhi shows a decreasing trend in an area with a loss of ~62.2 km2 or 63.9% of the total area during the past five decades. The hydrological dynamics of Lake Yakhi during the last 50 years show its shift into a playa lake coinciding with the local climate changes in warming since 1987 and drying since 1992. In the lake's margin, mafic igneous provenance indicates a derivation from weathered granite and gneiss terrains on the oceanic island arc. However, in the lake's center, felsic igneous and quartzose sedimentary provenances show a derivation from the pre-existing sedimentary terrain on the active continental margin. Lake Yakhi sediments show the granite (felsic) and granite basalt (felsic to mafic) source rocks with mostly shale and arkose. The A-CN-K ternary plot shows that granites, granodiorites, and tonalities dominated in the lake sediments may have been transported from the source rocks enriched in plagioclase and feldspars. The weathering trend in the source area shows a low degree of chemical weathering and the chemical maturity shows a climatic shift from semiarid to arid climatic conditions in the Lake Yakhi basin.